A 200mph supercar powered by the devil’s own fuel? Could a sworn petrolhead ever love the Audi R8 V12 TDI?

A perplexed look has written itself all over my face, and as much as I feel I should, I can’t hide it from the chap sitting next to me. It’s the sort of shock you get when you go to pick up what looks like a heavy box and discover that it’s feather-light. What’s just happened is that I’ve started the Audi R8 V12 TDI for the first time.

It was a fairly easy process – this being a concept car there’s no key, just a big red (sort of faded metallic red, almost dusky pink) starter button on the right hand spoke of the steering wheel. Press it once and it warms the coils whilst the needles do a sweep of the dials. Then hold it down for a second and the engine does something behind you. It doesn’t erupt, fire, explode, brum, chunter or even rattle into life, it sort of zizzes. At idle it’s making a thin, high-pitched whirring noise almost like an electronically synthesised imitation of what an engine might sound like. It seems a truly bizarre sound for a 6-litre V12 to be making, but cleverly it is also a very clean sound, which I’m sure is music to the ears of the boys and girls marketing diesel as the future…

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Some introductions are required. The chap sitting next to me in the pink shirt and two-week Miami tan is the splendidly named Thomas Kräuter, head of concept fabrication. This is his baby, his creation, so it must take the patience of a saint to sit next to a bunch of journalists from all over the globe as they ride his clutch. Then there’s Cara, the state trooper who will very kindly be shutting down sections of road for our photographs. She has a sidearm, so we’ll be very nice to her.

Next up, the car. This is the same one that was shown for the first time at the Detroit motor show in January but repainted from matt silver to this rather snazzy red. It’s the same one because it is the only one and therefore, if not priceless, very very expensive. The chassis is stock R8. The engine, however, is based on the race-winning V12 from the R10 Le Mans car and hence has all Audi’s diesel know-how contained within it.

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The crankcase is made from cast iron mixed with vermicular graphite, which is 40 per cent more rigid and 100 per cent more fatigue-resistant than ordinary cast iron. Common-rail technology is used for the injection system, two pumps building pressure up to 2000bar in the rails. Revised piezo injectors with eight-hole nozzles then feed the fuel into the cylinders. Piezo crystals expand in a fraction of a millisecond when an electrical voltage is applied, which means that the number of injections during an operation cycle can be increased (up to five in the V12 TDI). The advantage of this is that you can have pilot injections, which tone down the ‘acoustic harshness’ of a diesel engine, and post injections, which help increase the temperature of the exhaust gases for the benefit of the particulate filters (of which more in a bit). The engine’s compression ratio is a whopping 16-to-1 and the two variable-turbine-geometry turbos, which sit on the outside of the V, generate up to 2.6bar of boost.

The end result of all this, and what you really want to know, is that the engine produces a monstrous 1000Nm or 737lb ft of torque from 1750 to 3000rpm. Almost as a sideshow there’s 500bhp to play with as well.

Apart from a millimetre here or there, Thomas says that the overall dimensions of the R8 haven’t changed from the V8 production car. The V12 is a bit of a squeeze lengthways and the firewall has had to be moved forward into the cabin by 70mm (although not to the detriment of occupant space). But as the V has an included angle of 60 degrees as opposed to 90 with the 4.2 V8 it actually sits slightly lower and the car’s overall weight distribution has been marginally improved. Part of that improvement is down to the gearbox, which is smaller than the petrol R8’s. How can it be smaller and cope with 700lb ft of torque, you ask? Well it can’t, is the unfortunate answer. It’s actually a gearbox from an A4 in this prototype and as a result the torque has been electronically halved to 369lb ft. With the full complement, Thomas reckons that the clutch plates and gearbox teeth wouldn’t last 100 metres…

The dense, 80-degree heat soaking through the glass roof panels combined with the disorientating effects of jet lag would probably be enough to make driving a small hatchback slightly surreal at the moment. But I’m driving the world’s first supercar to sip diesel, a concept that ten years ago seemed laughable and frankly pretty ghastly (to most of us, anyway). Which makes the whole experience seem very weird indeed. For our first foray we’re just driving up and down a stretch of disused tarmac near the waterfront. There have been dire reports about how many revs we’ll be restricted to and that if we go above 30mph then Cara will use her sidearm in ways you don’t want to imagine. So we start off gingerly. It takes barely any revs to roll away from a standstill and even with an artificial cap on the torque you can still feel the huge potential simmering just below the surface. The gearbox has a slightly heftier feel than the petrol but there’s still that wonderful metallic sound like a sword being brought swiftly out of a scabbard as you slice across the open gate.

I dare a few more revs and a bit more speed as Thomas isn’t whimpering yet. We’re up to about 45mph now and approaching some pigeons. Now, pigeons are actually quite intelligent birds, even in America, but as the big red car with the gleaming grille (actually the same size as the production car’s grille but it looks bigger without the number plate) bears down on them they continue to peck and not fly. I’m not sure if Thomas likes Tom Lehrer, so I decide to slow down, at which point it occurs to me that the reason the birds haven’t scattered is probably because they simply can’t hear the R8 coming. Eventually they mosey out of the way but I suspect more because they don’t like the sudden arrival of some shade.

Next we head out onto the smoother, quieter road nearby so that Andy can get some photographs. Cara the state trooper swings into action and sets up a rolling blockade with blues lit while various people with walkie-talkies manage the traffic with the sort of airwave chat that only Americans do. Through first and second I can use most of the throttle travel and, although in its emasculated form the TDI doesn’t exactly leap forward, the way it zips through the revs and requires another gear is astonishing. You rush through the first two gears almost too quickly for comfort and it’s a tricky process balancing the flaring revs and all that torque as you try to make smooth progress back down the ’box. As Thomas says, it would make more sense with an automatic but Audi couldn’t put an auto into a one-off sports car. Fortunately the engineers are working on a DSG, which should suit the car perfectly.

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For all its race pedigree it’s a smooth engine too. Thomas suggests I try his favourite 30mph sixth-gear test and sure enough there is absolutely no judder or grumble, just a smooth increase in speed. It’s a superb demonstration of the huge reserves of the engine behind us.

Just above and to the right of my head I can hear the NACA duct on the roof working as it forces air into the two beautifully arching carbon beams that feed the turbos and which I can see in the rear view mirror. After a few passes we come back to base and I thumb the red button again to shut the engine down. As you’d expect given the race engine on which it’s based on, the V12’s revs just stop. All that’s left is a drawn-out sucking noise like Darth Vader inhaling deeply or a plumber inspecting a leaky boiler before giving you a quote.

The two other journalists with us are keen to get into the car, partly because one of them has a to catch a flight back to the UK rather urgently. Through the morning they take their turns pottering around, but you never hear them leave or arrive back. If you’re the sort of person who wants the antithesis of a Lambo with a Tubi then this is the car for you. There’s so much going on in the exhaust system it’s no wonder it’s rather like watching a silent movie. First there’s the oxidising catalyst, then there’s the particulate filter to make sure there are no big bad black PR clouds coming out of the back, and finally there’s a special catalytic converter where small quantities of an aqueous urea (stop giggling) solution called AdBlue are injected. The hot gases mingle with AdBlue, which breaks down into ammonia, which then splits nitric oxides down into nitrogen and water. As a result the engine already meets Euro 6 emissions regs (not due until 2014) and gives money to a polar bear sanctuary, probably.

Although it doesn’t have the aural drama of its Sant’Agata cousin, the R8 certainly makes up some ground in the looks department. Where the current V8 R8 looks almost delicate, the concept appears to have been bulking and toning in a gym. As it prowls round the Miami waterfront it looks particularly good from the front, but I also love the way the signature ‘sideblades’ are flared outwards. The intakes they cover are 30 per cent larger on the TDI and scoop up air for the intercoolers now housed behind them to gorge on. Although the concept has the same ride height as the production R8, the lower side-skirts make it look even more groundhugging and accentuate what are apparently extensive underbody aerodynamics. The skirts also house two new small vents to help cool the huge ceramic brakes. The R8 TDI looks slightly more functional and less elegant from the back, where there is necessarily a lot of the hexagonal mesh to help the heat escape from the tightly packed engine bay.

As the other journos head for the airports, I agree to stay behind and help one of the photographers with his shots. Thomas seems quite happy about my driving now, and I’m about to get probably the best illustration that anyone outside Audi has had of the effect of 150kg of extra engine on the R8’s wonderful dynamics. Using the machined aluminium collar that surrounds the start/stop button, there are three dynamic modes to choose from: ‘Dynamic’ is default, ‘Sport’ hones the magnetic ride dampers and sharpens the already electric throttle response (come to think of it, they did plug the car in several times during the day… perhaps it was all an elaborate hoax and this is in fact the world’s first hybrid supercar?), while ‘Race’ puts the rear wing up permanently and makes the normally white instrument lighting glow bright red.

Cara the state trooper rolls out onto the freeway and holds back the stream of evening traffic, leaving me with three empty lanes to swoop back and forth across for the camera. In Dynamic the TDI feels a touch softer on its springs than the production R8, but the precision is definitely still there. Firm up the dampers and it’s business as usual, the R8 slicing accurately from central reservation to hard shoulder, staying flat and composed. As I dive straight from a left to a right swoop there’s no sense of the greater mass creating any moments of awkward transition; they really have made this work.

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We play on the freeway for another ten minutes or so; it doesn’t take much to coax out of Thomas what the R8 TDI is like on the limit round a circuit (and as someone who spent many years on chassis development before he moved to his current position he should know). Apparently, despite expectations, it doesn’t fall into lift-off oversteer any more easily than the normal R8, yet with little provocation from the right pedal it will oversteer all day long. Apparently, someone once returned this unique car with its flanks covered in grime after finding themselves with five minutes to spare, freezing tarmac and an empty car park. Grinning from ear to ear, Thomas motions the time-honoured body language for oversteer.

By the time the R8 V12 TDI is safely packed back into its trailer there is absolutely no doubt that Audi could deliver a hugely impressive diesel supercar to the showrooms, and in a very short timeframe. All they have to do is indoctrinate the pub bragger in the ways of torque as well as power. And convince the likes of us of the joys of the silent supercar.